1. Field of the Invention
The present invention relates to a power element mounting substrate, a method of manufacturing the same, a power element mounting unit, a method of manufacturing the same, and a power module, which are used in a semiconductor device for controlling high current and high voltage.
2. Background Art
As shown in the below-listed Patent Document 1, such a power module generally includes a power element mounting substrate and a power element. The power element mounting substrate includes a circuit layer brazed on a surface of a ceramic plate. The power element is soldered to a front surface of the circuit layer. The circuit layer and the power element are conventionally soldered using a PbSn-containing solder material. Recently, however, so-called lead-free solder materials which contain no Pb are used widely from the environmental point of view.
As shown in the below-listed Patent Documents 2 and 3, in order to reduce total thermal resistance in a stacking direction, such a power module recently includes a power element mounting unit. In the power element mounting unit, a circuit layer is brazed to a front surface of a ceramic plate, and a cooler having a cooling channel formed therein is brazed to a back surface of the ceramic plate. The total thermal resistance of the power module is reduced by the structure in which the cooler is brazed directly to the back surface of the ceramic plate with no other member disposed therebetween.
As shown in the below-listed Patent Document 2, in order to reduce total thermal resistance in a stacking direction, some power modules recently include a power element mounting unit with a circuit layer brazed to a front surface of a ceramic plate, and a cooler brazed to a back surface of the ceramic plate. The total thermal resistance of the power module is reduced by the structure in which the cooler is brazed directly to the back surface of the ceramic plate with no other member disposed therebetween.
In this case, the cooler is constituted using an Al alloy and includes a top plate section having a surface to be brazed to the ceramic plate, and a pending section provided to suspend from a surface opposite to the surface to be brazed.
The cooler may include, other than the top plate section and the pending section, a bottom plate section provided in parallel with the top plate section and connected to the pending section. The cooler may include a refrigerant supply channel surrounded by the top plate section, the pending section and the bottom plate section. Alternatively, the cooler may include no bottom plate section, and include the top plate section and the pending section. Plural pending sections used as pins or fins may be provided on a surface opposite to the surface to be brazed in the top plate section.
As shown in the below-listed Patent Document 4, a known power module includes a power element mounting substrate and a power element. The power element mounting substrate includes a circuit layer brazed to a front surface of a ceramic plate, and a heat block which is constituted using a pure Cu or Cu alloy and is soldered to a front surface of the circuit layer. The power element is soldered to a surface of the heat block. With the heat block, heat conducted from the power element to the heat block via the solder layer is immediately distributed in a surface direction of the heat block so as to prevent temperature rise in the power element.    Patent Document 1: WO 03/090277    Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H4-363052    Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2004-115337    Patent Document 4: Japanese Patent No. 3044952